1. Field of the Invention
The present invention relates to improvements in ducting for acoustical speakers and enclosures and more particularly, but not by way of limitation, to a three-purpose duct which is acoustically coupled with a speaker diaphragm whether active or passive, for dampening low-frequency ringing, acoustically isolating the diaphragm and acoustically loading the diaphragm for lower frequency response.
2. History of the Prior Art
The use of quality sound systems in both the home and in businesses are often times limited by the size limitations on the speaker enclosures and hence, there has been considerable effort to achieve big sound while utilizing a small enclosure. Various types of ducting has been accomplished in connection with the speaker enclosures in an attempt to effectively extend the frequency response curve at the low end.
Since low frequency response is largely dependent on the loud speaker system resonance, current designs usually rely on an enclosure that is proportionally large in relation to the driver. Stated another way, the larger the enclosure, the lower the frequency resonance. The driver, or any other moving piston in connection with the enclosure represents an enclosure opening. The smaller the enclosure opening is, again the lower the resonance is. Therefore, reducing the enclosure size means reducing the driver size as well if low frequency performance is to be maintained.
However, in the case of small enclosures, the driver size must be too small to be an efficient radiator if low frequency performance is the objective. Also, power handling ability is decreased with the use of small drivers. Therefore, it is a practice of most small loud speaker system designs to use a larger driver in order to keep efficiency reasonable, trading low frequency performance as a result of the larger effective enclosure openings.
Increasing the mass of a larger speaker in order to obtain lower frequency response has been accomplished by adding a papier mache weight to the center of the speaker cone on a conventional speaker so that that speaker may be used in a smaller enclosure. The addition of weight lowers the resonance of the speaker so that when it is coupled to an enclosure the added mass to the loud speaker diaphragm will help to lower the overall resonance of the loud speaker and enclosure together. Although the added weight lowers the resonance of the loud speaker, its ability to reproduce higher frequencies has been traded for the lower resonance.
Often times additional openings will be provided in the enclosure and are connected to ducting within the enclosure in order to tune the overall resonance of the system while allowing the energy from the rear of the loud speaker cone to be added to the front wave which has met with reasonable success.
Another conventional device to further tune the enclosure is by the addition of a passive radiator which serves to transfer sound into the surrounding outside area.
Another problem associated with the use of large speaker assemblies or passive radiators for that matter, is the tendency for these large diaphragms to continue ringing after the electrical signal has been terminated from the driver.
The added weight to the speaker cone hereinbefore mentioned actually increases the system ringing and, as stated, results in a significant sacrifice in the speaker's ability to reproduce higher frequencies with the added weight.
The patent to Pitre, U.S. Pat. No. 4,031,318, issued June 21, 1977 for "High Fidelity Loudspeaker System" shows ducting surrounding the speaker but does not reduce the effective area of the opening.
In summary, the various attempts at providing big sound with small speaker enclosures has met with, at best, limited success.